Apparatus for rectification of high-tension alternating current



June 26, 1928. 1,675,057

'w. A. SCHMIDT APPARATUS FOR RECTIFICATION OF HIGH TENSION ALTERNATING CURRENT Filed July 19- 1920 Inventor: \Nalcev fl chmidf b7 CmIlaJ/P Ma /17fflfivrney Patented June 26, 1928.

UNITED STATES PATENT OFFICE.

WALTER A. SCHMIDT, OF LOS ANGELES, CALIFORNIA, ASSIGNOR TO INTERNATIONAL PRECIPITATION COMPANY, OF 'LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIA.

APPARATUS FOR RECTIFICATION HIGH-TENSION ALTERNATING CURRENT.

Application filed July 19,

This invention relates to means for rectifying alternating current in electrical circuits presenting high potential difference, and particularly where such current is subject to sudden fluctuations, as, for example, in connection with apparatus, such as used for the electrical precipitation of fumes from gases. In operating such electrical precipitators with the usual types of current rectifying apparatus, the current fluctuations tend to establish electric surges and oscillations which interfere with the efiicient operationof such precipitation apparatus. Such electrical precipitators are usually energized, under high potential stress, with unidirectional current obtained by rectification of the alternating current of a high tension alternating circuit by means of a mechanical rectifier, or rotating circuit closing means, operated in synchronism with such alternating current. In operating such apparatus it has been found that under certain conditions there is a tendency for the current to surge or oscillate, more or less violently, particularly at or near the times of making and breaking circuit, and the resulting disturbances in the electric current usually result in lower precipitator efiiciency and consequent decreased operating capacity of the precipitating apparatus. Such oscillations are, in general, due to resonance or similar effects in the electric circuit by reason of the considerable capacity and conductance of the load, acting as a leaky condenser. The high tension circuit thus presents the necessary factors of capacity, inductance and conductance to develop oscillations which-in practice often become very severe. These electrical oscillations, in some cases, interfere with the operation of the precipitating apparatus by causing current discharge within the precipitation'apparatus in a direction opposite to the direction for normal opdration thereby reducing the precipitation 'efiiciency, both by reason of repeatedly reversing the direction of translation of'the fume or dust particles suspended in the gas within the precipitator, and by lowering the effective voltage that can be maintained between the electrodes comprising the precipitator. These phenomena are associated, particularly, with the precipitation of certain classes of suspended material, and the disturbing efi'ects thereof become 1920. Serial No. 897,389.

especially serious when operating electrical precipitators of large capacity in conjunction with current supplying and rectifying units of correspondingly large output.

A further objectionable efi'ect of such oscillations or surges in the electric circuit is the liability of damage to the insulation of the transformer and other apparatus in the circuit.

The main object of the present invention is to provide for overcoming the disturbing efi'ects above described by segregating the oscillations essentially into that portion of the circuit in which they may be readily damped out. These disturbing oscillations are largely of high frequency, and it is the oscillations of high frequency which are part'cularly objectionable and which it is particularly desired to eliminate.

Another object of the invention is to provide means for reducing the resistance at the circuit contacts or shoes of the mechanical rectifier so as to provide for a less violent break down of the air gap at said shoes, and thereby decrease the surging action.

The accompanying drawings illustrate an embodiment of my invention, and referring thereto:

Fig. 1 is a transverse section of the Fi 2 1s a longitudinal section of the recti er shown in Fig. 1;

Fig 3 is a longitudinal section of one of the shoes of the rectifier;

Fig. 4 is a transverse section thereof;

Fig. 5 is a transverse section of a modified form of shoe;

Fig. 6 is a diagrammatic perspective of a modified form of the rectifier.

Referring to Figs. 1 and 2 the rectifier therein shown comprises a shaft 1 mounted to rotate on bearings 2 and connected to the synchronous motor or generator 3 and thereby operated in synchronism with the alternating current to be rectified, segments or conductors 4 and 5 carried by and insulated from said shaft, said segments being preferably mounted on an insulating disc 13, and stationary shoes 6, 7, 8 and 9, supported adjacent to the path of motion of said segments or conductors 4 and 5. In order to tion of such stationary shoes ar und the axis of rotation of the shaft 1, said shoes may be mounted by insulating bars 10 on spiders or frames 11, carried by hubs 12, which are mounted to turn on the bearings 2 aforesaid, the angular position of the frame constituted by spiders 11 and bars 10 being adjusted by any suitable means, for example, by a hand wheel 14, connected to a gear wheel 15, engaging a segment gear wheel 16 on one of the hubs 12. To support the shoes 7, etc., with requisite stiffness the insulating bars 10 .are preferably provided in pairs, and the said shoes are mounted by screw stems 17 thereof, screwing through blocks 18, clamped on said bars by screws 19. By adjustment of the screw stem 17 by means of nuts 17 thereof the radial position of the shoes 6, 7, etc., and the distance thereof from the path of the rotating conducting segments 4 may be varied according to requirements.

In order to avoid possibility of the rotating parts striking the shoes at the high speed required, it is necessary to provide a clearance or gap so that the current in passing from the stationary shoes to the rotating segments has to jump this air gap. This involves a certain amount of resistance, and this resistance rapidly increases as the retating conductors or segment-s move away from opposing relation to the stationary shoes. A variable air gap resistance is thus introduced into the high tension circuit which must be broken down before current 1 can be transmitted to the load, so as to break the circuit. The violence of the breakdown of this air gap resistance tends, in the case of loads having considerable conductance and capacity, to produce oscillations or surges in the circuit which not only endanger the insulation in the transformer and other parts, but seriously interfere with the .efliciency of precipitation of the electrical precipitator. To avoid or minimize this effect, and also to reduce the effective resistance of the gap connection at the shoes .of the rectifier, I prefer to provide means for maintaining in or adjacent to such gap, a

zone of comparatively low resistance produced by the maintenance of a conducting vapor in such zone, as, for example, through the volatilization of a solid or solution 'giving a vapor of relatively high electrical conductivity. For this purpose, each of the shoes 7, or any number of said shoes, may be provided with means for receiving and holdother alkaline material, or volatile metallic salt. For convenience in retaining this material in place the said pocket 20 may be filled with a porous material indicated at 27, such as plaster of Paris, molded in place and impregnated with a solution of sodium chloride, or other salt, such solution being supplied continuously or intermittently, for example, as shown in Fig. 4, from a reservoir 21, under control of a valve 22, or, as

shown in Fig. 5, from a wick 55, leading from a reservoir 56. Or solid sodium chloride, or other substance capable of forming a vapor under the action of the arc, may be embodied or incorporated in the porous material in recess 20. Or the vapor forming material may be supplied to the shoe in any other manner.

In order to further reduce the objectionable efiects of surges and oscillations in the electric load circuit, on interruption-of current of rectifier, I prefer to so arrange and connect the shoes of the rectifier to the load or rectified portion of the circuit and the supply or alternating portion of the circuit that the surging due to the interruption will be essentially confined to a limited portion of the circuit, and,,as in electrical precipitation apparatus, one of the two sets of opposing electrodes is usually electrically grounded, I prefer to thus confine the oscil lations to the ground connect-ion of the electrical circuit. For this purpose, the connection shown in Fig. 1 may be adopted, two of the shoes 6 and 7 being connected by wires 24: and 25, respectively, through choke coils 41 and 42 to opposite sides of the high tension coil 26 of 'a'step-up transformer whose low tension coil 29 is connected to the wires 30 and 31, respectively, of an alternating current circuit; shoe 8 being connected by wire 33 to one side of the load, for example, to the high tension-discharge electrode system 34 of an electrical precipitator, the opposing low tension electrodes 35 thereof being electrically grounded at 36 and the remaining shoe 9 of the rectifier being connected by wire 38 to a resistance 39, having a grounded connection 40, preferably adjustable so as to provide for regulation of the resistance. Shoe 9 is preferably shorter than shoe 8, While shoes 6 and 7 are of intermediate length and are asymmetrically placed with respect to shoes 8 and 9. By havingthe shoes so constructed and arranged, electrical contact is made in the grounding leg of the circuit after such connection is made in the load portion of the circuit, and is interrupted in the grounding leg of the circuit, before it is interrupted in the load portion of the circuit.

. In the operation of the apparatus abovedescribed, the shaft 1 is rotated in synchronism with the current to be rectified, for example, by means of an alternating current motor or generator connected thereto in well known manner and indicated at 3, and as the respective segments 4 and 5 pass the pairs of shoes 68 and 79, they connect or bridge said shoes so as to establish connection alternately from each of the line wires 24 and 25 to the load wire 33 or the ground connection 38 as the case may be. Thus, in the position shown in Fig. 1 of the drawings, the current will pass from the side of the transformer 26, which, for the time being, is of high negative potential through choke coil 41, wire 24, shoe 6, segment 4, shoe .8, wire 33, electrical precipitator 34 and 35, and to ground at 36, and from ground the connection is continued through the connection 40, resistance 39 and wire 38 to shoe 9 and thence through segment 5, shoe 7, wire 25 and choke coil 26 of the transformer.

larly the circuit is also closed only in the grounding leg of the circuit. At the moment of make and break, surges or oscillations are set up in the circuit, said oscillations being distributed in difierent parts of the circuit in accordance with the resonance of such portions. As a result oscillations may be set up in the circuit as a Whole and subsidiary oscillations may be set up in different portions of the circuit due to local capacity and inductance effects in such por tions; and these subsidiary oscillations are especially injurious and objectionable on account of the relative sharpness andintensity thereof. The surges with steep wave fronts will not pass through the transformers usually employed and thus, by making and breaking the current connections in the grounding leg of the circuit, the oscillations can be greatly reduced in the load leg of the circuit, and, when necessary, the oscillations can readily be damped out in such grounding leg of the circuit by the introduction of suitable resistance therein.

It will be noted that any oscillations of steep wave front, setlup between the transformer and the rectifier, are reflected by the choke coils 41 and 42, thus protecting the transformer coil from excessive potential strains due to such surges, and also localizing the objectionable surges or oscillations in that leg of the circuit in which contact is either made or broken.

Inasmuch as the circuit is first completely connected and first interrupted at the'shoes in the grounding leg of the circuit and as shoe 9 is connected to ground through re-- sistance 39,0scillations are rapidly damped, by the absorption of energy in resistance 39,

and the arcs drawn at the shoes are substantially non-oscillatory in character.

The current passing between the shoes 8" and the segments of the rotary members of the rectifier is only interrupted after interruption at the shoe 9, so that there is no arcing at this shoe. The provisions of the means above described for causing production of alkaline vapors in the gaps or zones of current flow adjacent the several shoes, decreases the resistance of such ga s and further reduces the tendency to pro uction of disruptive discharge at these gaps.

The stationary shoes are preferably placed as close to the path of the rotating segments as is consistent with mechanical safety and on account of the very small air gap and the relatively high conductivity thereof, and an account of the intense ionlzation of the alkali vapors present, the flow of current is comparatively free and whatever oscillations may develop under special conditions, will be of low intensity. The heavy trailing arcs at the ends of the shoe are eliminated in the load portion of the circuit, such elimination being secured by the asymmetric arrangement of the rectifier shoes, as described.

The construction of the rectifier may be variously modified without departing from my invention, for example, as shown in Fig. 6, the interruption of the ground connection for the rectifier may be effected by a contact or circuit making member separate from the the shoe 49 being connected to a wire 38- leading to a resistance 39, which may be adjustable and is connected by wire 45 to a stationary conduct-or or shoe 43 located adj acent to the path of travel of a circuit breaking member, consisting, for example, of-

cross-arms 50 and 51 mounted on the shaft 1 or otherwise connected to rotate in synchronism with the reversing contact means 4 and 5, said arms 50 and 51 being grounded by means ofa brush 52, having a ground connection 53, and engaging with a collector ring 54 in metallic connection with the crossarms 50 and 51. In this form of the invention, the several contacts or shoes 46, 47 48 and 49 may all be of equal length and sufiici ently long to maintain cooperative relation with the respective rotative segments 4 and 5 durlng the times required for'the periodic circuit connection for rectification of the required portion of each wave and -for a short time thereafter, and the contact or shoe 43 is so positioned and of such length that the circuit connection to ground from shoe 49 through resistance 39, shoe 43, cross-arm 50 or 51, collector ring 54, brush 52 and connection 53 will be interrupted at the gap between shoe 43 and cross-arm 50 or 51 before the respective segments 4 and 5 pass out of circuit making relation with the respective Shoes 46, 47, 48 and 49.

What I claim is:

1. The combination, with a load having considerable capacity and conductance and having a ground connection, and with an alternating current supply means of considerable inductance, of a rectifier provided with contacts for establishing and breaking connection with said load, with contacts for establishingand breaking connections with said current supply means, and with contacts for establishing and breaking a ground connection, and means for operating the rectifier in synchronism with the alternating current, the contacts. of the rectifier being so arranged as to establish the said ground connection of the rectifier after the other connections of the rectifier are established.

2. The combination, with a load having considerable capacity and conductance and having a ground connection, and with an alternating current supply means of considerable inductance, of a rectifier provided with contacts for establishing and breaking connection with said load, with contacts for establishing and breaking connection with siderable inductance, of a rectifier provided with contacts for establishing and breaking connection with said load, with contacts for establishing and breaking connection with said currentsupply means, and with contacts for establishing and breaking a ground connection, and meansfor operat ing the rectifier in synchronism with the alternating current, the contacts of the rectifier being so arranged as to establish the ground connection of the rectifier after the other ,connections of the rectifier are established, and to break said ground connection of the rectifier before said other connections of the rectifier are broken.

4. In a rectifier, a rotary rectifier member provided with a conductor, a stationary shoe arranged adjacent to the path of said condu tor to make and break connection therewith through an air gap, a perforate member on said shoe, and means for supplying a liquid containing a volatile substance to said perforate member.

' In testimony whereof I have hereunto subscribed my name this 2nd day of July, 1920. WALTER A. SCHMIDT. 

